Method for producing coke, and coke

ABSTRACT

A method for producing a coke includes performing dry distillation of a mixture. The mixture includes: an ashless coal; an oxidized ashless coal obtained by an oxidation treatment of an ashless coal; and a raw petroleum coke. Relative to 100 parts by mass of a total of the ashless coal, the oxidized ashless coal and the raw petroleum coke, a content of the ashless coal is from 5 to 40 parts by mass, and a total content of the ashless coal and the oxidized ashless coal is from 30 to 70 parts by mass.

TECHNICAL FIELD

The present invention relates to a method for producing a coke, and acoke. More specifically, the present invention relates to a method forproducing a coke suitable as a reducing material for non-ferrousmetallurgy, and a coke.

BACKGROUND ART

Conventionally, a coke has been used as a reducing material in refiningof a non-ferrous metal such as aluminum and titanium. In particular, acalcine coke (so-called calcined coke) obtained by heating a rawpetroleum coke is inexpensive and therefore, is used for generalpurposes.

The raw petroleum coke as a raw material of the calcine coke is aby-product generated in the process of refining petroleum from crudeoil. Accordingly, the character of the calcine coke is dependent on thecrude oil. For example, the impurities (e.g., sulfur, nickel, vanadium,sodium and the like) contained in the calcine coke are derived from thecrude oil as a raw material of the calcine coke. These impurities becomea contamination source and therefore, in the case of using the calcinecoke as a coke for use in refining, the content of the impurities (inparticular, sulfur content; hereinafter the same) is required to be assmall as possible. However, since the impurity content in the recentlyproduced crude oil is large, it has been difficult to provide a cokewith a small impurity content.

As regards a carbon material with a small impurity content, studies arebeing made to utilize, as the coke raw material, an ashless coalsubstantially containing no ash. For example, Patent Document 1discloses a production method of an ashless coal to be used for a fuel,a coke raw material, a chemical raw material, etc.

However, the ashless coal has high thermal fluidity and has a propertyof melting at 200 to 300° C. irrespective of the grade of the rawmaterial coal. In addition, the ashless coal has a property of expandingwhen it is heated at around 400° C. Therefore, when an ashless coal issubjected to forming, followed by dry distillation by high-temperatureheating, the ashless coal melts, and the shape of the formed productcannot be maintained, leading to a problem with thermoplasticity.Furthermore, expandability is a problem, for example, as follows: theashless coal may expand by undergoing foaming due to high-temperatureheating to overflow from a dry distillation apparatus or adhere to theinner wall of the dry distillation apparatus, making its dischargeimpossible, or the coke may be obtained as a sponge-like porous body andextremely reduced in the bulk specific gravity. In this way, because ofthe problem with thermoplasticity or expandability, the ashless cokecould be hardly used as a coke raw material.

To solve such a problem, the present inventors have proposed a techniquefor modification of the ashless coal (Patent Document 2). Specifically,a production method of a carbon raw material is disclosed, the methodincluding a slurry heating step of heat-treating a slurry containing acoal and an aromatic solvent, a separation step of separating the slurryheat-treated in the slurry heating step into a liquid component havingdissolved therein coal and a solid component composed of an ash andinsoluble coal, an ashless coal obtaining step of obtaining an ashlesscoal by removing the aromatic solvent from the liquid component, and anashless coal heating step of heat-treating the ashless coal obtained inthe ashless coal obtaining step to provide a carbon raw material,wherein the volatile content of the carbon raw material obtained in theashless coal heating step, as measured by the method specified in JIS M8812, is less than 35 mass % and 24 mass % or more.

According to this technique, by virtue of including a slurry heatingstep, a separation step, an ashless coal obtaining step, and an ashlesscoal heating step for adjusting the volatile content to fall in apredetermined range, a low-ash carbon material having excellentself-sinterability can be produced.

PRIOR ART LITERATURE Patent Documents

Patent Document 1: JP-A-2001-26791

Patent Document 2: JP-A-2009-144130

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

The technique of Patent Document 2 produces an excellent effect inimproving self-sinterability, but since modification of the ashless coalrequires a lot of labor, the productivity is not necessarily high, andthe modified ashless coal is relatively expensive.

The present invention has been made by focusing on the above-describedcircumstances, and an object of the present invention is to provide amethod for producing a high-purity coke at a lower cost than everbefore, and to provide a high-purity coke.

Means for Solving the Problems

The method for producing a coke in the present invention which iscapable of achieving the object includes performing dry distillation ofa mixture containing: an ashless coal; an oxidized ashless coal obtainedby an oxidation treatment of an ashless coal; and a raw petroleum coke,in which, relative to 100 parts by mass of a total of the ashless coal,the oxidized ashless coal and the raw petroleum coke, a content of theashless coal is from 5 to 40 parts by mass, and a total content of theashless coal and the oxidized ashless coal is from 30 to 70 parts bymass.

Preferable embodiments of the present invention include the case wherethe mixture is subjected to forming, and then, the dry distillation isperformed, the case where a percentage of increase in oxygen of theoxidized ashless coal is from 2 to 10%, the case where the oxidationtreatment is an air oxidation, and the case where the oxidationtreatment is performed at a temperature of 150° C. or more and less thanan ignition point.

In addition, the preferable embodiments include the case where the drydistillation is performed in a chamber furnace, and the case where thedry distillation is performed in a rotary kiln.

An aspect of the present invention includes a coke produced byperforming dry distillation of a mixture, the mixture containing: anashless coal; an oxidized ashless coal obtained by an oxidationtreatment of an ashless coal; and a raw petroleum coke, in which,relative to 100 parts by mass of a total of the ashless coal, theoxidized ashless coal and the raw petroleum coke, a content of theashless coal is from 5 to 40 parts by mass, and a total content of theashless coal and the oxidized ashless coal is from 30 to 70 parts bymass.

Advantage of the Invention

According to the production method in the present invention, ahigh-purity coke can be produced at a low cost by using a raw petroleumcoke. In addition, in the present invention, a high-purity coke can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for explaining one example of the productionprocess of an ashless coal.

FIG. 2 is a flowchart for explaining one example of the productionprocess of a coke in the present invention.

MODE FOR CARRYING OUT THE INVENTION

The present inventors have made many intensive studies to provide ahigh-purity coke at a low cost by using a raw petroleum coke as a carbonraw material, and found the followings.

The impurity content of the ashless coal is very small, and mixing ofthe ashless coal with the raw petroleum coke is useful for reducing theimpurity content of the coke. However, as pointed out in conventionaltechniques, an ashless coal has a problem with thermoplasticity orexpandability.

Studies of the present inventors revealed that when the ashless coal issubjected to an oxidation treatment, the thermoplasticity andexpandability of the ashless coal can be improved. However, the oxidizedashless coal is in the form of fine powder and exhibits low caking, anddry distillation of a mixture of the oxidized ashless coal and the rawpetroleum coke causes a problem that the coke obtained becomes powderyand readily scatters out of a dry distillation apparatus and inaddition, the bulk specific gravity of the coke is reduced. Intensivestudies have been made to solve such a problem, and as a result, it hasbeen found that when a mixture of an ashless coal, an oxidized ashlesscoal and a raw petroleum is made, the ashless coal functions as a binderfor binding the oxidized ashless coal and the raw petroleum coke and aproblem such as powdering of the coke can be suppressed.

It has been then found that when a mixture containing the ashless coal,the oxidized ashless coal and the raw petroleum coke each with apredetermined content described later is used, the coke obtained can beprevented from melting or expanding and a high-purity coke could beprovided at a low cost.

The coke production method in the present invention is described belowby referring to the flowcharts illustrated in FIGS. 1 and 2.

First, the ashless coal used in the present invention is described.

An ashless coal indicates a coal having an ash content of 5 mass % orless, preferably 3 mass % or less. The ashless coal is preferably a coalin which the ash concentration of a residual inorganic material (e.g.,silicic acid, alumina, iron oxide, lime, magnesia, alkali metal or thelike) when heated at 815° C. to thereby form an ashed body thereof isvery low. Specifically, the ash concentration is more preferably 5,000ppm or less (on the mass basis), still more preferably 2,000 ppm orless. In addition, the ashless coal is absolutely water-free andexhibits higher thermal fluidity than the raw material coal.

<Production Process of Ashless Coal>

The ashless coal can be obtained by various conventional productionmethods and, for example, may be obtained by removing a solvent from asolvent extract of a coal. For example, the ashless coal can be obtainedthrough the following steps S1 to S3 (see, FIG. 1), but the ashless coalproduction process (S1 to S3) described below may be appropriatelychanged, and various treatment steps may be added, if desired.

For example, in the production of an ashless coal, as long as each ofthe above-described steps is not adversely affected, other steps, e.g.,a coal pulverization step of pulverizing the raw material coal, aremoval step of removing an unwanted material such as refuse, or adrying step of drying the obtained ashless coal, may be provided betweenrespective steps above or before or after each step.

<Slurry Heating Step: S1>

The slurry heating step (S1) is a treatment of mixing a coal and anaromatic solvent to prepare a slurry and heat-treating the slurry toextract a coal component in the aromatic solvent.

The kind of the coal as a raw material (hereinafter, sometimes referredto as “raw material coal”) is not particularly limited. For example,various known coals such as bituminous coal, subbituminous coal, browncoal and lignite can be used. In view of profitability, it is morepreferable to use a low-rank coal such as subbituminous coal, brown coaland lignite, instead of using an expensive high-grade coal such asbituminous coal.

The aromatic solvent is not particularly limited as long as it is asolvent having a property of dissolving a coal. Examples of the aromaticsolvent include a monocyclic aromatic compound such as benzene, tolueneand xylene, and a bicyclic aromatic compound such as naphthalene,methylnaphthalene, dimethylnaphthalene and trimethylnaphthalene. Inaddition, examples of the bicyclic aromatic compound include aliphaticside chain-containing naphthalenes, biphenyl, and a long-chain aliphaticside chain-containing alkylbenzene. In the present invention, a bicyclicaromatic compound that is a non-hydrogen-donating solvent, is preferred.

The non-hydrogen-donating solvent is a coal derivative that is a solventprimarily purified from a carbonization product of a coal and mainlycomposed of a bicyclic aromatic compound. The reason why anon-hydrogen-donating solvent is preferred is that thenon-hydrogen-donating solvent is stable even in a heated state andexcellent in the affinity for a coal and therefore, the ratio of a coalcomponent in the solvent (hereinafter, sometimes referred to as“extraction percentage”) is high and in addition, because the solventcan be easily recovered by distillation or other methods andfurthermore, the solvent recovered can be cyclically used.

If the boiling point of the aromatic solvent is too low, the pressurerequired during heating extraction or in the later-described separationstep (S2) would be high, and the loss due to volatilization in the stepof recovering the aromatic solvent is increased, leading to a decreasein the recovery ratio of the aromatic solvent. Furthermore, a decreasein the extraction percentage during heating extraction is caused. On theother hand, if the boiling point of the aromatic solvent is too high,separation of the aromatic solvent from a liquid component or a solidcomponent in the separation step (S2) is difficult, and the recoveryratio of the solvent lowers. The boiling point of the aromatic solventis preferably from 180 to 330° C.

The coal concentration relative to the aromatic solvent is notparticularly limited. Although it may vary depending on the kind of theraw material coal, if the coal concentration relative to the aromaticsolvent is low, the ratio of the coal component extracted in thearomatic solvent to the amount of the aromatic solvent would be small,and this is not profitable. On the other hand, a higher coalconcentration is better, but if the coal concentration is excessivelyhigh, the slurry viscosity would be increased, and transfer of theslurry or separation between a liquid component and a solid component inthe separation step (S2) is likely to become difficult. The coalconcentration, on the dry coal basis, is preferably 10 mass % or more,more preferably 20 mass % or more and preferably 50 mass % or less, morepreferably 35 mass % or less.

If the heat treatment (heating extraction) temperature of the slurry istoo low, the bonding between molecules constituting the coal cannot besufficiently weakened, and in the case of using a low-rank coal as theraw material coal, the resolidification temperature of the ashless coalobtained in the later-described ashless coal obtaining step (S3) cannotbe elevated. On the other hand, if the heat treatment temperature is toohigh, the pyrolytic reaction of the coal would be very active to causerecombination of pyrolytic radicals produced, leading to a decrease inthe extraction rate. The slurry heating temperature is preferably 350°C. or more, more preferably 380° C. or more, and preferably 420° C. orless.

The heating time (extraction time) is not particularly limited, but ifthe extraction time is long, the pyrolysis reaction proceedsexcessively, allowing for the progress of a radical polymerizationreaction, and the extraction ratio lowers. For example, at the aboveheating temperature, the heating time is preferably 120 minutes or less,more preferably 60 minutes or less, still more preferably 30 minutes orless, and preferably 10 minutes or more.

After the heating extraction, the extract is preferably cooled to 370°C. or less so as to suppress a pyrolysis reaction. The lower limit ofthe temperature when cooling is preferably 300° C. or more. If cooled toless than 300° C., the dissolving power of the aromatic solvent isreduced, and reprecipitation of the once extracted coal componentoccurs, leading to a decrease in the yield of ashless coal.

The heating extraction is preferably performed in a non-oxidizingatmosphere. Specifically, the heating extraction is preferably performedin the presence of an inert gas such as nitrogen. This is becausecontact with oxygen during heating extraction is risky due to a fear ofignition and when hydrogen is used, the cost rises.

The pressure in the heating extraction may vary depending on thetemperature during heating extraction or the vapor pressure of thearomatic solvent to be used, but if the pressure is lower than the vaporpressure of the aromatic solvent, the aromatic solvent is vaporized andnot confined in a liquid phase, and extraction cannot be achieved. Onthe other hand, if the pressure is too high, the equipment cost andoperation cost are increased, and this is not profitable. The preferablepressure is generally from 1.0 to 2.0 MPa.

<Separation Step: S2>

The separation step (S2) is a step of separating the slurry heat-treatedin the slurry heating step (S1) into a liquid component and a solidcomponent. The liquid component is a solution containing the coalcomponent extracted in the aromatic solvent. The solid component is aslurry containing an ash insoluble in the aromatic solvent and aninsoluble coal.

The method for separating the slurry into a liquid component and a solidcomponent in the separation step (S2) is not particularly limited, and aconventional separation method such as filtration method, centrifugalseparation method and gravity settling method, may be employed. In thepresent invention, it is preferable to use a gravity settling methodenabling continuous operation of a fluid and being low-costly andsuitable for treatment of a large amount. In the case of employing agravity settling method, a liquid component (hereinafter, sometimesreferred to as “supernatant liquid”) that is a solution containing acoal component extracted in the aromatic solvent can be obtained fromthe upper part of a gravity settling tank, and a solid component(hereinafter, sometimes referred to as “solid content concentrate”) thatis a slurry containing a solvent-insoluble ash and a coal can beobtained from the lower part of the gravity settling tank.

Subsequently, as described below, the aromatic solvent is separated andrecovered from the supernatant liquid by using a distillation method,etc., and as a result, ashless coal having a very low ash concentrationcan be obtained (ashless coal obtaining step (S3)).

<Ashless Coal Obtaining Step: S3>

The ashless coal obtaining step (S3) is a step of separating thearomatic solvent from the supernatant liquid to obtain an ashless coalhaving a very low ash concentration.

The method for separating the aromatic solvent from the supernatantliquid is not particularly limited, and a general distillation method,evaporation method (e.g., spray drying method), etc. can be used. Thearomatic solvent recovered by separation can be repeatedly used. By theseparation and recovery of the aromatic solvent, the ashless coal can beobtained from the supernatant liquid. The obtained ashless coal can beused as a raw material of the mixture in the present invention, and alsocan be used as a raw material of the oxidized ashless coal.

<Other Steps>

If desired, a byproduct coal in which the ash is concentrated may beproduced by separating the aromatic solvent from the solid contentconcentrate (byproduct coal obtaining step). As the method forseparating the aromatic solvent from the solid content concentrate, ageneral distillation or evaporation method can be used, similarly to theabove-described ashless coal obtaining step (S3) of obtaining an ashlesscoal from a liquid component.

<Production Process of Coke>

The production method of the coke in the present invention is describedbelow by referring to FIG. 2. In the production of the coke, as long aseach step is not adversely affected, other steps, e.g., a pulverizationstep of pulverizing various raw materials, etc., a removal step ofremoving an unwanted material such as refuse, or a step of applyingvarious treatments to the obtained coke, may be provided betweenrespective steps or before or after each step.

<Oxidation Step: C1>

The oxidation step is a step of applying an oxidation treatment to theashless coal to obtain an oxidized ashless coal. By applying anoxidation treatment to the ashless coal, the ashless coal is modified,and the thermoplasticity or expandability can be improved.

The method for oxidizing an ashless coal is not particularly limited. Itis desirable to perform oxidation in an oxidizing atmosphere such asoxygen, ozone, nitrogen dioxide and air, and air oxidation using oxygenin air as an oxidizer is preferred.

The percentage of increase in oxygen of the oxidized ashless coal is notparticularly limited, but if the percentage of increase in oxygen is toolow, the modification effect on the ashless coal is not sufficient, anda problem attributable to thermoplasticity or expandability is sometimescaused during the dry distillation. On the other hand, if the percentageof increase in oxygen is too high, the yield is reduced, and as aresult, this is not profitable. Accordingly, the percentage of increasein oxygen is 2% or more, preferably 3% or more, and is preferably 10% orless, more preferably 5% or less.

In the present invention, when the percentage of increase in oxygen ofthe ashless coal is set, an ashless coal having a lower percentage ofincrease in oxygen than the set value is not dealt with as the oxidizedashless coal in the present invention even if the ashless coal has beensubjected to an oxidation treatment. In addition, in the case where anashless coal having a lower percentage of increase in oxygen than theset value is used as a carbon raw material, the ashless coal is dealtwith as the ashless coal in the present invention,

The percentage of increase in oxygen as used in the present invention isa value obtained by measuring the oxygen content percentage of anashless coal before and after oxidation treatment according to JIS M8813(Calculation Method of Oxygen Percentage) and making calculation (oxygencontent percentage of oxidized ashless coal-oxygen content percentage ofashless coal).

The temperature kept during oxidation (hereinafter, oxidationtemperature) may be appropriately adjusted so that the desiredpercentage of increase in oxygen can be obtained. If the oxidationtemperature is low, the ashless coal may be insufficiently oxidized, andthe above-described modification effect may not be fully exerted. Inaddition, if the oxidation temperature is low, a long time is requiredto achieve the desired percentage of increase in oxygen, and theproductivity is reduced. On the other hand, if the oxygen temperature istoo high, the oxidation rate is excessively increased, and the oxidationdegree of the ashless coal can be hardly controlled. The oxidationtemperature is preferably 150° C. or more, more preferably 200° C. ormore, and is preferably less than the ignition point of the ashlesscoal, more preferably 350° C. or less.

The oxidation time (holding time at a predetermined temperature) may beappropriately adjusted so that the desired percentage of increase inoxygen can be obtained. If the oxidation time is short, the ashless coalmay be insufficiently oxidized. On the other hand, if the oxidation timeis long, the ashless coal may be excessively oxidized, and the yield isreduced to cause an increase in the cost. For example, the oxidationtime in the above-described temperature range is preferably 0.5 hours ormore, more preferably 1 hour or more, and is preferably 6 hours or less,more preferably 3 hours or less. After the oxidation, the ashless coalmay be allowed to cool to room temperature.

The particle diameter (equivalent-circle diameter; hereinafter, the sameapplies to the particle diameter) of the ashless coal subjected to anoxidation treatment is not particularly limited. If the particlediameter of the ashless coal is too large, the inside of the ashlesscoal may not be sufficiently oxidized, leaving a fear of occurrence ofmelting, etc. during the dry distillation. On the other hand, if theparticle diameter of the ashless coal is too small, the handlingproperty is deteriorated. The average particle diameter of the ashlesscoal is preferably 3 mm or less, more preferably 1 mm or less, and ispreferably 0.2 mm or more, more preferably 0.3 mm or more. From thestandpoint of accelerating the oxidation, the maximum particle diameteris also preferably 3 mm or less, more preferably 1 mm or less, stillmore preferably 0.5 mm or less.

<Carbon Raw Material Mixing Step: C2>

The carbon raw material mixing step is a step of mixing the ashlesscoal, the oxidized ashless coal, and a raw petroleum coke, therebyobtaining a mixture (hereinafter, referred to as “mixed carbon rawmaterial”).

The raw petroleum coke is a solid substance by-produced, in thepetroleum refining process, together with light oil in equipment (coker)for producing light oil by heating a distillation residue at a hightemperature (for example, at 500° C. or more) to cause pyrolysis. In thepresent invention, as for the raw petroleum coke, various known rawpetroleum cokes available on the market can be used. A raw petroleumcoke having a volatile content of 5 to 20 mass % and a sulfur content of2 to 5 mass % is preferred.

In the present invention, the mixing ratio of the ashless coal in themixed carbon raw material and the mixing ratio between the ashless coaland the oxidized ashless coal must be appropriately controlled accordingto the properties of the ashless coal (oxidized/non-oxidized, oxidationdegree) so as to produce a high-purity coke.

(I) Content of Ashless Coal: From 5 to 40 Parts by Mass

If the mixing ratio of the ashless coal is too small, the function as abinder is not sufficiently exerted, and the coke becomes powdery. On theother hand, if the mixing ratio of the ashless coal is too large,thermoplasticization or expansion due to the ashless coal becomesexcessive and, for example, the coke may be obtained as a sponge-likeporous body and reduced in the bulk specific gravity, or the coke mayadhere to the inner wall of a dry distillation apparatus, making itsdischarge impossible.

In the present invention, the content of the ashless coal is 5 parts bymass or more, preferably 10 parts by mass or more, and is 40 parts bymass or less, preferably 25 parts by mass or less, per 100 parts by massof the total of the ashless coal, the oxidized ashless coal, and the rawpetroleum coke.

(II) Total Content of Ashless Coal and Oxidized Ashless Coal: From 30 to70 Parts by Mass

As described above, the total content of the ashless coal is 40 parts bymass or less, but by containing the oxidized ashless coal, the amount ofthe raw petroleum coke used can be more decreased, and the impuritycontent in the coke can be more reduced. The ashless coal and oxidizedashless coal are more expensive than the raw petroleum coke andtherefore, when the total content of those is increased, the unit costof the coke rises. On the other hand, if the total content of theashless coal and oxidized ashless coal is too low, the effect ofreducing impurities is not sufficiently obtained. For this reason, thetotal content of the ashless coal and oxidized ashless coal is 30 partsby mass or more, preferably 35 parts by mass or more, more preferably 40parts by mass or more, and is 70 parts by mass or less, preferably 65parts by mass or less, more preferably 60 parts by mass or less, per 100parts by mass of the total of the ashless coal, the oxidized ashlesscoal and the raw petroleum coke.

The content of the oxidized ashless coal is not particularly limited,but if the content of the oxidized ashless coal is too small, there iscaused a problem that, for example, the coke expands to have asponge-like structure or melts and sticks in an apparatus. Therefore,the content of the oxidized ashless coal is preferably 5 parts by massor more, more preferably 10 parts by mass or more, still more preferably30 parts by mass or more, per 100 parts by mass of the total of theashless coal, the oxidized ashless coal and the raw petroleum coke. Onthe other hand, the upper limit of the content of the oxidized ashlesscoal may be appropriately adjusted to fall in the above-described rangeof the total content of the ashless coal and the oxidized ashless coal(from 30 to 70 parts by mass) but it is preferably 50 parts by mass orless, more preferably 40 parts by mass or less.

The average particle diameter of the ashless coal is not particularlylimited, but if the average particle diameter of the ashless coal is toolarge, a non-uniformity may be produced in the mixed state of themixture, not allowing the ashless coal to fully exert a binder effect,etc. On the other hand, if the average particle diameter is too small,the handling property may be deteriorated. The average particle diameterof the ashless coal is preferably 10 mm or less, more preferably 0.5 mmor less, and is preferably 0.1 mm or more, more preferably 0.2 mm ormore. If the maximum particle diameter of the ashless coal is too large,a non-uniformity may be produced in the mixed state in a formed product,and for this reason, it is preferably 1.0 mm or less, more preferably0.5 mm or less.

In addition, the average particle diameter of the ashless coal ispreferably smaller than the average particle diameter of the oxidizedashless coal, because a gap between carbon raw materials is filled andthe binder effect is more enhanced.

The mixture in the present invention may be sufficient if it containsthe ashless coal, the oxidized ashless coal, and the raw petroleum coke,and the mixture may contain other material(s) (for example, a knownadditive such as a binder and a petroleum pitch) as long as the presentinvention is not adversely affected, but in the case of containing othermaterial(s) in the mixture, the impurity content of the coke may beincreased due to the other material(s). Therefore, the total of theashless coal, the oxidized ashless coal and the raw petroleum coke inthe mixture is preferably 90 mass % or more, more preferably 100 mass %.The 100 mass % indicates that the mixture consists of the ashless coal,the oxidized coal and the raw petroleum coke and the remainder isimpurities.

The method for mixing the ashless coal, the oxidized ashless coal andthe raw petroleum coke is not particularly limited, and a conventionalmethod ensuring uniform mixing may be employed. Examples thereof includea mixer, a kneader, a single-shaft mixer, and a double-screw mixer.

<Forming Step: C3>

The forming step is a step of forming, if desired, the mixture obtainedin the carbon raw material mixing step (C2) into a desired shape toobtain a formed product. By making a formed product from the mixture,binding between respective carbon raw materials can be more firmlycreated due to the binder effect of the ashless coal, and powdering ofthe coke or reduction in the bulk specific gravity can be suppressed.

For example, in the case of dry distillation of the mixture in a chamberfurnace, a load applies in the vertical direction, reducing the distancebetween respective carbon raw materials, and respective carbon materialsare bound by the binder effect of the ashless coal, so that the coke canbe prevented from powdering and the bulk specific gravity can beincreased. Such an effect can be more enhanced by making a formedproduct.

On the other hand, in the case of dry distillation of the mixture by useof a horizontal furnace in which a sufficient load does not apply in thevertical direction, such as rotary kiln, the binder effect is not fullyexerted. As a result, binding between respective carbon raw materials isweak, and the coke is likely to be powdered, leading to a reduction inthe bulk specific gravity of the coke. Therefore, the mixture ispreferably formed into a desired shape before the dry distillation.

The method for making a formed product from the mixture is notparticularly limited and examples thereof include, for example, a methodusing a double roll (twin roll)-type forming machine by means of flatrolls or a double roll-type forming machine having an almond-shapedpocket, a method using a single-shaft press-type forming machine orroller-type forming machine or an extrusion forming machine, and pressforming by means of a mold, and any of these methods can be employed.Among them, it is preferable to make a briquette-like formed product orsheet-like formed product by means of a double roll-type briquetter,roll compaction, etc.

Forming of the mixture may be cold forming that is performed at aroundroom temperature, but hot forming performed under heating is preferred.When the mixture is formed under pressure at a high temperature, theashless coal is plastically deformed to fill voids between the oxidizedashless coal particles and the raw petroleum cokes, so that a morehighly densified formed product can be obtained. In turn, a coke havinga higher bulk specific gravity can be obtained by dry distillation ofthe highly densified formed product. On the other hand, if the formingtemperature is too high, the ashless coal may be softened and expanded,failing in achieving a high bulk specific gravity. The hot formingtemperature (the temperature of a device such as mold or roll) ispreferably 100° C. or more, more preferably 200° C. or more, and ispreferably 450° C. or less, more preferably 300° C. or less. The formingpressure is not particularly limited, and conventional conditions may beemployed. For example, the forming pressure is approximately from 0.5 to3 ton/cm².

<Dry Distillation Step: C4>

The dry distillation step is a step of performing dry distillation ofthe mixture obtained in the carbon raw material mixing step (C2) or theformed product obtained in the forming step (C3), thereby acquiring acoke. The shape of the furnace used for dry distillation is notparticularly limited, and dry distillation may be performed batchwise byusing a chamber furnace or dry distillation may be performedcontinuously by using a vertical shaft furnace. In addition, ahorizontal rotary furnace such as rotary kiln may also be used.

As for the dry distillation conditions, conventional conditions may alsobe employed, and the dry distillation temperature may be appropriatelyset and is not particularly limited but may be preferably 650° C. ormore, more preferably 700° C. or more, and preferably 1,200° C. or less,more preferably 1,050° C. or less. The dry distillation time at the drydistillation temperature is not particularly limited as well, and adesired dry distillation time may be set according to the apparatusconfiguration, etc. and may be preferably 5 minutes or more, morepreferably 10 minutes or more, and preferably 24 hours or less, morepreferably 12 hours or less.

The dry distillation atmosphere may be a non-oxidizing gas atmosphere soas to prevent deterioration of the coke due to oxidation. As thenon-oxidizing gas, various known gases may be used, and the gas may be,for example, an inert gas such as nitrogen, helium and argon, or areducing gas such as hydrogen gas.

During dry distillation, not only the raw petroleum coke is converted tocalcine coke (calcined coke) but also the ashless coal acts as a binderbetween the oxidized ashless coal and the calcine coke to firmly bondthe oxidized ashless coal to the calcine coke, thereby enhancing thecoke strength.

In the case of subjecting the mixture to dry distillation, respectivecarbon raw materials are bound to each other, and amorphousagglomerate-shaped coke is obtained. In addition, when the mixture isformed, the coke having substantially the same shape as that of theformed product before dry distillation is obtained. In the coke in thepresent invention, the blending ratio of the ashless coal isappropriately controlled, so that the coke can be kept from adhering tothe inside of the dry distillation apparatus, which makes its dischargeimpossible, and also from powdering.

The thus-obtained coke has higher purity and higher bulk specificgravity than those of conventionally known coke. Specifically, thecontent of minerals that become impurities is preferably 1 mass % orless, more preferably 0.5 mass % or less. The bulk specific gravity ispreferably 0.53 g/cm³ or more, more preferably 0.6 g/cm³ or more, stillmore preferably 0.7 g/cm³ or more, and most preferably 0.8 g/cm³ ormore. The sulfur content is preferably 2 mass % or less.

In addition, the mixture is free from the above-described problemattributable to thermoplasticity or expandability during the drydistillation and in turn, the coke obtained is excellent in theappearance and can be discharged from the dry distillation apparatus.

As described above, the coke produced by performing dry distillation ofa mixture containing the ashless coal, the oxidized ashless coalobtained by an oxidation treatment of an ashless coal, and the rawpetroleum coke, in which, relative to 100 parts by mass of the total ofthe ashless coal, the oxidized ashless coal and the raw petroleum coke,the content of the ashless coal is from 5 to 40 parts by mass and thetotal content of the ashless coal and the oxidized ashless coal is from30 to 70 parts by mass, is a coke having a high purity and a high bulkdensity and succeeded in improving the above-described thermoplasticityand expandability which may emerge as a problem in the case of using anashless coal.

Examples

The present invention is described more specifically below by referringto Examples, but the present invention is, of course, not limited to thefollowing Examples and may be carried out by appropriately makingchanges as long as they are in conformity to the gist describedhereinabove and hereinafter, all of which are included in the technicalscope of the present invention.

(Production of Ashless Coal) (Slurry Heating Step: S1)

With 5 kg of the raw material coal (bituminous coal), an aromaticsolvent (1-methylnaphthalene (produced by Nippon Steel Chemical Co.,Ltd.)) in an amount (20 kg) four times that of the raw material coal wasmixed to prepare a slurry. This slurry was pressurized with nitrogen of1.2 MPa and subjected to a heat treatment (heating extraction) in anautoclave having an internal volume of 30 liter under the conditions of370° C. and 1 hour.

(Separation Step: S2)

The obtained slurry was separated into a supernatant liquid and a solidcontent concentrate in a gravity settling tank maintained at the sametemperature and pressure.

(Ashless Coal Obtaining Step: S3)

The obtained supernatant liquid was further filtered (stainless meshfilter with an opening size of 1 μm) to obtain an ashless coal solution.The aromatic solvent was separated and recovered from the ashless coalsolution by a distillation method to produce an ashless coal. Theobtained ashless coal was pulverized so as to pass through a sievehaving an opening size of 3 mm, whereby the ashless coal was obtained.

(Measurement of Sulfur Content)

This ashless coal was measured for the sulfur concentration by themethod specified in JIS M 8122. As a result, the sulfur content of theashless coal was 0.5 mass %.

(Production of Coke) (Oxidation Step: C1)

A part of the ashless coal was pulverized so as to pass through a sievehaving an opening size of 0.5 mm. The pulverized ashless coal was heatedin an air atmosphere to a predetermined temperature shown in Table 1 andheld at the same temperature for a predetermined time, therebyperforming an oxidation treatment (in Table 1, “Oxidation Conditions”).After the oxidation treatment, the ashless coal was allowed to cool toroom temperature, whereby an oxidized ashless coal was obtained.

Here, the ashless coal and the oxidized ashless coal were measured forthe oxygen concentration before and after the oxidation treatment,according to JIS M 8813, and the percentage of increase in oxygen of theoxidized ashless coal was calculated. The results are shown in Table 1(in Table 1, “Percentage of Increase in Oxygen”).

(Raw Petroleum Coke)

Commercially available raw petroleum coke (volatile content: 9.5 mass %,sulfur content: 3.1 mass %) was pulverized so as to pass through a sievehaving an opening size of 10 mm.

(Carbon Raw Material Mixing Step: C2)

Ashless coal (“A” in the Table), oxidized ashless coal (“B” in theTable), and raw petroleum coke (“C” in the Table) were mixed in apredetermined ratio shown in Table 1 (in Table 1, “Blending Ratio of RawMaterials”) to obtain a mixture.

Here, in No. 16, the ashless coal subjected to the oxidation treatmentwas dealt with as an ashless coal, because the percentage of increase inoxygen was less than 2% (1.50%). Accordingly, although the blendingratio of No. 16 was A:B:C=50 (20 mass % of ashless coal not subjected toan oxidation treatment+30 mass % of ashless coal having a percentage ofincrease in oxygen of 1.5%):0:50, in order to show details of theblending ratio of No. 16, for convenience sake, the blending ratio(“20”) of the ashless coal not subjected to an oxidation treatment isshown in column A of the Table, and the blending ratio (“30”) of ashlesscoal having a percentage of increase in oxygen of 1.5% despite havingbeen subjected to an oxidation treatment is shown in column B.

(Forming Step: C3)

With respect to a part of the mixtures (Nos. 7 to 12 and 15; in theTable, “Presence or Absence of Forming”=done), a formed product wasproduced under the following conditions:

Forming method: roll compaction method

Roll temperature: 100° C.

Roll diameter: 162 mm

Roll width: 60 mm (pyramid-shaped groove)

Inter-roll width: 2 mm

Roll rotational speed: 15 rpm

Linear pressure: 3 ton/cm

(Dry Distillation Step: C4)

The mixture (Nos. 1 to 6, 13, 14 and 16 to 25) and the formed product(Nos. 7 to 12 and 15) were subjected to a dry distillation treatment ina chamber furnace (Nos. 1 to 6 and 15 to 25) or in a kiln (Nos. 7 to14).

(Dry Distillation Treatment in Chamber Furnace)

The mixture (Nos. 1 to 6 and 16 to 25) or the formed product (No. 15)was added into a graphite crucible having an inner volume of 1,000 mL toprovide a bulk specific gravity of 0.85 g/cm³, followed by heating to1,000° C. at a rate of 3° C./min in a nitrogen atmosphere, and held atthe same temperature for 5 hours to perform dry distillation, therebyproducing a coke.

(Dry Distillation Treatment in Rotary Kiln)

The mixture (Nos. 13 and 14) or the formed product (Nos. 7 to 12) wasinserted into a heated rotary kiln (diameter: 200 mm, total length:4,000 mm) at an insertion rate of 1 kg/l. As for the heating temperatureof the rotary kiln, the temperature was adjusted to an inlet temperatureof 400° C. and an outlet temperature of 1,000° C. It was held at thetemperature above for 60 minutes in a nitrogen atmosphere to perform drydistillation, thereby producing a coke.

(Evaluation Method)

The obtained coke was measured for bulk specific gravity, sulfurcontent, appearance, and presence or absence of adhering to the insideof the apparatus.

(Bulk Specific Gravity) (in the Table, “Bulk Specific Gravity after DryDistillation (g/cm³)”)

A wooden cubic container whose one side is 100 mm was filled with thecoke, and the bulk specific gravity was determined from the dry mass(W:g) of the coke which had been filled with the container. In thisExample, the coke was judged to be passed when the bulk specific gravitywas 0.53 g/cm³ or more.

(Sulfur Content) (in the Table, “Sulfur Content after Dry Distillation(%)”)

The sulfur concentration of the coke was measured in the same manner asfor the ashless coal. In this Example, the coke was judged to be passedwhen the sulfur content was 2.0% or less.

(Appearance, Presence or Absence of Adhering to Inside of Apparatus) (inthe Table, “Coke Characteristics”)

The appearance of the coke was observed with an eye and evaluated. Inthe case of performing dry distillation treatment in a chamber furnace(Nos. 1 to 6 and 15 to 25): the coke that was agglomerate-shaped wasjudged as “Excellent” (in the Table, “PE”); the coke that wasagglomerate-shaped but slightly expanded (the bulk specific gravity:0.53 g/cm³ or more and less than 0.7 g/cm³) was judged as “Pass” (in theTable, “P”); the coke that was powdery was judged as “Fail” (in theTable, “F”); and the coke that adhered and could not be discharged (inthe Table, “FA”) or that expanded (in the Table, “FB”), was also judgedas “Fail”. The appearance is ranked in the order of PE>P>(F, FA, FB).

In the case of performing dry distillation treatment in a kiln (Nos. 7to 14): the coke that was flaky and free from occurrence of expansion,cracking, chipping or powdering was judged as “Pass” (in the Table,“P”); the coke that was powdery or experienced expansion, cracking,chipping or powdering was judged as “Fail” (in the Table, “F”); and thecoke that adhered and could not be discharged was also judged as “Fail”(in the Table, “FA”). The appearance is ranked in the order of P>(F,FA).

TABLE 1 Blending Bulk Specific Sulfur Percentage Ratio of Gravity AfterContent of Raw Materials, Presence or Dry Dry After Dry OxidationIncrease in A/B/C Absence of Distillation Distillation Distillation CokeNo. Conditions Oxygen (mass %) A + B Forming Method (g/cm³) (%)Characteristics  1 200° C., 1 h 3% 4/48/48 52 none chamber furnace 0.451.6 F  2 200° C., 1 h 3% 5/47/48 52 none chamber furnace 0.75 1.7 PE  3200° C., 1 h 3% 10/40/50 50 none chamber furnace 0.72 1.7 PE  4 200° C.,1 h 3% 20/30/50 50 none chamber furnace 0.79 1.7 PE  5 200° C., 1 h 3%40/10/50 50 none chamber furnace 0.63 1.7 P  6 200° C., 1 h 3% 42/10/4852 none chamber furnace 0.49 1.5 FB  7 200° C., 1 h 3% 4/48/48 52 donekiln 0.39 1.6 F  8 200° C., 1 h 3% 5/47/48 52 done kiln 0.58 1.6 P  9200° C., 1 h 3% 10/40/50 50 done kiln 0.74 1.7 P 10 200° C., 1 h 3%20/30/50 50 done kiln 0.81 1.6 P 11 200° C., 1 h 3% 40/10/50 50 donekiln 0.53 1.6 P 12 200° C., 1 h 3% 42/10/48 52 done kiln — 1.5 FA 13200° C., 1 h 3% 10/40/50 50 none kiln 0.40 1.7 F 14 200° C., 1 h 3%20/30/50 50 none kiln — 1.6 FA 15 200° C., 1 h 3% 20/30/50 50 donechamber furnace 0.81 1.6 PE 16 200° C., 0.3 h 1.50%   20/30*/50 50 nonechamber furnace 0.52 1.7 FB 17 200° C., 0.5 h 2% 20/30/50 50 nonechamber furnace 0.67 1.7 P 18 300° C., 0.5 h 6% 20/30/50 50 none chamberfurnace 0.77 1.6 PE 19 300° C., 1 h 10%  20/30/50 50 none chamberfurnace 0.72 1.5 PE 20 200° C., 1 h 3% 20/20/60 40 none chamber furnace0.79 1.8 PE 21 200° C., 1 h 3% 20/10/70 30 none chamber furnace 0.82 1.9PE 22 200° C., 1 h 3% 20/5/75 25 none chamber furnace 0.81 2.1 PE 23200° C., 1 h 3% 20/40/40 60 none chamber furnace 0.89 1.3 PE 24 200° C.,1 h 3% 20/50/30 70 none chamber furnace 0.92 1.1 PE 25 200° C., 1 h 3%20/60/20 80 none chamber furnace 0.91 0.8 PE

As shown in Table 1, in Nos. 2 to 5, 8 to 11, 15, 17 to 21, 23 and 24satisfying the predetermined requirements of the present invention, thecoke was of high purity with a sulfur content of 2.0% or less, and thebulk specific gravity thereof was also high. In addition, expansion,etc. during the dry distillation treatment were sufficiently suppressed,and the coke characteristics were good. Here, in No. 5 where theblending ratio of the ashless coal was high, the coke slightly expanded.In No. 17 where the percentage of increase in oxygen was lower thanother cases, modification of the oxidized ashless coal was inferior toother cases, and the coke slightly expanded.

No. 1 is the case where the blending ratio of the ashless coal was low.In this case, since the content of the ashless coal functioning as abinder was small, the coke was powdered by the dry distillationtreatment.

No. 6 is the case where the blending ratio of the ashless coal was high.In this case, since the content of the ashless coal was large, expansionoccurred during the dry distillation treatment to not only yieldsponge-like (porous) coke but also greatly reduce the bulk specificgravity.

No. 7 is the case where the blending ratio of the ashless coal was low.In this case, since the content of the ashless coal was small, powderingoccurred in the kiln during the dry distillation treatment.

No. 12 is the case where the blending ratio of the ashless coal washigh. In this case, not only the ashless coal was melted during the drydistillation but also the formed product was foamed and expanded, and asa result, the coke adhered to the inner wall of the kiln and could notbe discharged.

No. 13 is the case where the mixture was not subjected to forming andthe powder was directly subjected to dry distillation in the kiln. Inthis case, since an adequate pressure was not applied to the mixtureduring the dry distillation, the oxidized ashless coal and the rawpetroleum coke could not be sufficiently bound and the coke remained ina powder form.

No. 14 is the case where the mixture was not subjected to forming andthe powder was directly subjected to dry distillation in the kiln. Inthis case, the oxidized ashless coal and the raw petroleum coke couldnot be sufficiently bound, similarly to the case of No. 13, and sincethe ashless coal content was increased and larger than the case of No.13, the coke adhered to the inner wall of the kiln due to melted andexpanded ashless coal and could not be discharged.

No. 16 is the case where the oxidation time was short relative to theoxidation temperature and in turn, the percentage of increase in oxygenwas low. In this case, since the content of the ashless coal (the totalof the ashless coal and the ashless coal which had been subjected to anoxidation treatment but having a percentage of increase in oxygen ofless than 2.0%) was too large without containing the oxidized ashlesscoal in which the percentage of increase in oxygen of the ashless coalis 2.0% or more, the ashless coal was foamed and expanded during the drydistillation treatment, and the bulk specific gravity was reduced.

No. 22 is the case where the blending ratio of the raw petroleum cokewas large. In this case, the sulfur content after dry distillation waslarge, and the purity of the coke was low.

No. 25 (Reference Example) is the case where the blending ratio of theraw petroleum coke was small. In this case, the coke having a smallsulfur content and a high bulk specific gravity was obtained, but sincethe blending ratio of the raw petroleum coke was small, the coke wasexpensive.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope of the invention.

This application is based on Japanese Patent Application No. 2013-251219filed on Dec. 4, 2013, the contents of which are incorporated herein byway of reference.

INDUSTRIAL APPLICABILITY

In the present invention, the coke suitable, e.g., as a reducingmaterial for non-ferrous metallurgy can be produced at a low cost.

1: A method for producing a coke, comprising performing dry distillationof a mixture containing: an ashless coal; an oxidized ashless coalobtained by an oxidation treatment of an ashless coal; and a rawpetroleum coke, wherein, relative to 100 parts by mass of a total of theashless coal, the oxidized ashless coal and the raw petroleum coke, acontent of the ashless coal is from 5 to 40 parts by mass, and a totalcontent of the ashless coal and the oxidized ashless coal is from 30 to70 parts by mass. 2: The method for producing a coke according to claim1, wherein the mixture is subjected to forming, and then, the drydistillation is performed. 3: The method for producing a coke accordingto claim 1, wherein a percentage of increase in oxygen of the oxidizedashless coal is from 2 to 10%. 4: The method for producing a cokeaccording to claim 1, wherein the oxidation treatment is an airoxidation. 5: The method for producing a coke according to claim 1,wherein the oxidation treatment is performed at a temperature of 150□Cor more and less than an ignition point. 6: The method for producing acoke according to claim 1, wherein the dry distillation is performed ina chamber furnace. 7: The method for producing a coke according to claim2, wherein the dry distillation is performed in a rotary kiln. 8: A cokeproduced by performing dry distillation of a mixture, the mixturecontaining: an ashless coal; an oxidized ashless coal obtained by anoxidation treatment of an ashless coal; and a raw petroleum coke,wherein, relative to 100 parts by mass of a total of the ashless coal,the oxidized ashless coal and the raw petroleum coke, a content of theashless coal is from 5 to 40 parts by mass, and a total content of theashless coal and the oxidized ashless coal is from 30 to 70 parts bymass.